Good questions! There is some evidence for botox effectiveness in treating bfs-type symptoms: https://pubmed.ncbi.nlm.nih.gov/35302525/

I had almost constant twitching in my left deltoid before the injections, which kept me up at night and made my life pretty miserable. My shoulder responded to meds including gabapentin and pregabalin, but I didn't tolerate either well at all - even at the lowest doses, I had extreme fatigue, depression, "dullness" and feeling pretty slow.

I got injections all over the delt (it's a big muscle!) by a chronic pain physician, who I was referred to by my PCP. The procedure consists of a few minor pin pricks in the affected region. I would say it took about 2 days total for it to kick in, but indications are that it could take up to a couple of weeks for some. It didn't eliminate the fasciculations entirely, as I felt some vibrations over the course of the 12 weeks between injections, but the repeated painful spasms that kept me up at night stopped almost altogether until a few days before the second injection, when they began to return in a reduced form.